1. Field of the Invention
The present invention relates to a vibration-damping rubber adapted to be used in the suspension of a vehicle, such as a stabilizer bushing for holding a stabilizer bar and coil spring insulator for supporting a coil spring.
2. Description of the Related Art
Examples of the vibration-damping rubber useful for a suspension include a stabilizer bushing for holding a stabilizer bar adapted to be secured to a suspension arm.
As shown in FIG. 1, such a stabilizer bushing is generally composed of a thick-walled cylindrical resilient rubber body 10, in which a stabilizer bar S is adapted to be inserted. The resilient rubber body 10 has a flat top surface and radially projecting flanges 12 formed along or around the end edges thereof. An outer surface of the resilient rubber body 10, which is defined between the flanges 12, is adapted to be retained by a bracket 14 having a generally U-shaped cross-section. The bracket 14 is secured to a vehicle body (not shown) by inserting bolts in attaching holes 16 formed in both end parts thereof.
The resilient rubber body 10 is generally formed of a natural rubber but this, however, can result in a problem that occurs when a vehicle starts or when the working angle of the stabilizer bar S is great, the problem being that the inner surface of the resilient rubber body 10 and stabilizer bar S may displace relative to each other thereby generating noise. To overcome this problem, it has been proposed to compose the resilient rubber body 10 of a rubber having high sliding characteristics, thus reducing the sliding resistance against the stabilizer bar S and restraining the generation of noise. In this arrangement, however, when, as shown in FIG. 2, the resilient rubber body 10 displaces laterally to abut a curved part S1 of the stabilizer bar S, the resilient rubber body 10 may slip laterally relative to the bracket 14 due to a lateral force applied by the stabilizer bar S, which is caused by the coefficient of friction between the resilient rubber body 10 and the bracket 14 or vehicle body being small. To prevent this lateral slippage, it is possible to provide stoppers adjacent to the resilient rubber body 10. This arrangement, however, has problems that both the number of parts and manufacturing costs increase.
On the other hand, another type of stabilizer bushing has been known where a resilient rubber body is provided with a slide surface composed of a resin material in an inner surface thereof (Japanese Utility Model application laid-open No. Sho 63-39011, Japanese Patent application laid-open No. Sho 63-57310, for example). The stabilizer bushing thus arranged, however, has a problem that the overall spring constant increases due to the resin material having a stiffness higher than that of rubber. To reduce the spring constant, the resilient rubber body can be made from a soft material. This arrangement, however, lowers the durability of the material. The slide surface of resin material has another problem that when sand or the like intrudes between the slide surface and the stabilizer bar, abrasion may occur and noise may be generated.
Examples of the vibration-damping rubber for a suspension also include a coil spring insulator adapted to be interposed between a coil spring and a spring seat, which is generally composed of a vibration-damping rubber sheet of natural rubber having a ring-like configuration. Vibration-damping rubber sheet is fitted into a ring-shaped groove formed along a periphery of the spring seat, and an end of the coil spring is retained in a concave which is formed in the vibration-damping rubber sheet in a circumferential direction thereof.
To assemble the coil spring insulator thus arranged, it must be positioned between the spring seat and the coil spring. Since the coil spring insulator has a high coefficient of friction, and accordingly low sliding characteristics, conventionally, before assembling, the coil spring insulator has normally been coated with silicone or the like. This increases the number of manufacturing processes. In addition, when the effect of silicone disappears after assembling and the friction resistance increases, noise may be generated due to the slippage of the spring seat and coil spring relative to each other.
Furthermore, since the conventional coil spring insulator is made of a thin sheet material, apparent spring constant increases to lower driving comfort.
In another example of the coil spring insulator, to prevent interference with the coil spring, the coil spring insulator is formed in to a tube-like configuration and a coil spring is retained therewithin. The tube-like coil spring insulator is generally composed of an urethane material, and assembled by cutting the urethane tube open, inserting the coil spring into the cut tube, and closing the cut tube with an adhesive, thus requiring much time and labor for assembly. Furthermore, the coil spring insulator of urethane material has another problem that, when vibrations are input, it cannot give good driving comfort.